We propose to examine both cellular and humoral aspects of eicosanoid metabolism by endothelial cells (EC) and the cellular elements of blood in Sickle Cell Disease (SCD) since our preliminary studies suggest that eicosanoids may significantly contribute the pathophysiology of vaso-occlusion. We will focus additionally on the pathophysiology of the long term vessel complications in SCD as our previous work has suggested a role for the hydroxyeicosanoids (HETES) in modulating EC proliferation. Besides the role of sickle red cells in initiating vaso-occlusion, the episodic nature of this event may be precipitated or propagated by humoral - induced alterations in the microcirculation. Prostaglandins and thromboxanes can alter microcirculatory tone, and our preliminary evidence suggests that decreased prostacyclin production occurs during vaso-occlusion. Thus, an imbalance, causing a relative increase in the thromboxane/prostacyclin ratio could alter microcirculatory tone and favour vasoconstriction. We propose a definite in vitro and in vivo study of these metabolites in blood and urine in SCD. The biochemical alterations leading to abnormal prostacyclin production will also be ascertained at the cellular level. In addition to episodic vaso-occlusion, vascular cell (endothelial and smooth muscle) proliferation in the macro- and microcirculation is a long term complication of SCD leading to substantial morbidity and premature mortality. We have previously documented that the HETEs produced by the cellular elements of blood cause endothelial cell (EC) proliferation and neovascularization at levels achievable in vivo. Moreover, we now show that HETE(S) play a role in EC - red blood cell adherence, that both serum and urinary HETE(S) are increased in individuals with SCD, and that SCD serum and plasma in vitro possesses an increased ability to stimulate EC proliferation. We therefore propose detailed in vitro biochemical studies of EC proliferation in SCD and an elucidation of the role of HETE(S) in EC-red cell adherence. A comparative study of in vivo HETE production in selected SCD patient groups with appropriate controls will also be undertaken with the backup of meticulous clinical data. We predict that patients with marked elevations in HETE production will experience more frequent vaso-occlusion and/or earlier onset of organ dysfunction. In summary, we hypothesize that eicosanoids (cyclo and lipoxygenase products) play a role in both the episodic vaso-occlusion and the chronic EC proliferation that are the protein manifestations of SCD, and provide a link between these two disparate processes.